BALL MILL INSPECTION PROCEDURES

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General:

The process engineer should be the doctor  of the system

The “doctor” is required for:

1. implementation of “Health checks” > Regular action
2. urgent investigations of actual process problems> Non-regular action

This presentation focuses on the regular “Health check” procedure.

The “Health checks”consist of standard measurements on a frequent basis

“Healths checks” are important in order to

• build up a knowledge and data base about the system performance
• record data and display them in trends for easy and fast diagnostic of problems.

The Main Advantage : 

Knowledge basis allows to investigate the root cause of problems and to avoid problems by early reaction based on the trend results.

For each measurement make sure you have:

• design data of the machines/equipment available.
• constant/stable operation condition for at least 2 hours.
• recorded the actual operation data like:
• – Production rate [t/h], Product type, composition [M-%]
• – Actual and target fineness off product [[Blaine or Residue]]
• – Actual mass flow rate (e.g. separator grits, water demand,etc)
• -Electrical power consumption of the main equipment
• – Actual operation parameter of the main equipment (e.g. separator speed, damper positions)

Material Sampling 

Circuit material granulometry:

Sampling points

Longitudinal sampling:

Sampling points at crash stop:

Filling Degree 

Ball charge filing degree:

Measurement by free height:

1- Measure average internal g,diameter, Di

2-Measure height, h, in three different points along axis for each grinding compartment

For Best results the measurements takes place in an empty mill (mill feed stopped for approx. 10 min).

Mill material level: 

Inspection only at crash stop

Record the material level approx. each meter along axis

Mill internals condition:

Ball Charge 

Ball charge sampling:

Solution 1) Total sorting of ball charge

Solution 2) Analysing the actual grinding media composition by spot samples.

tromp curve:

Separator tromp curve:

Define the sampling points

Ventilation

Separator Ventilation:

Basics: Air flow measurement

Measurement points:

Weigh Feeder

a)Static calibration – feeder not in operation

• Zero-point – adjustment (local control box, no load)
• Span adjustment with calibration weight (local control box)

b)Calibration with feeder in operation (preferred if possible)

• operate weigh feeder with defined setpoint and load material into truck for e.g. 10 minutes, while mill is shut down
• weigh truck empty and loaded, calculate throughput and adjust controller if necessary

Instrument

Instrument Verification:

1. Electronically : Check and adjust zero-point and span with e.g. mA-transmitter
2. Operation check : Compare control room indication with local manual measurement of temperature, pressure and flow

>Adjust transmitters

Control loop Verification:

1- Operation check :

• record process parameters with control loop in operation over period of e.g. 6-8 hours with constant production
• record mill power consumption at counter KWh

Adjust control loop parameters if required

Information on:

• Available information at the CCR
• Control system
• Control strategy
• First impression on operation
• Circuit stability

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